Ab initio study of the energy loss near sulfur K and L 2,3 edges of layered MS 2 (M=Ta, Nb and V) in trigonal prismatic and octahedral structures.

This study set out to calculate the full-potential linearized augmented plane wave (FPLAPW)-based energy loss near sulfur K and L2,3 edge structures of group V layered transition metal disulfides MS2 (M=Ta, Nb, and V) in octahedral (1T) as well as trigonal prismatic (2H) structures. The calculations showed that, consistent with other calculations, all the studied materials were metallic due to the partially filled d bands in their configurations. Furthermore, the calculated ELNES spectra revealed a good agreement with the available experimental XANES analogues. The d-like and p-like transitions of M and sulfur atoms were the dominant electron transitions in K edge spectra. Spectrum characteristics of the sulfur L2,3 edge of ELNES indicated the transition of sulfur-p electrons to the unoccupied s or d states. These spectra reflect the electronic band structures of materials, as well. As the focus shifts from bulk to monolayer, substrate hybridization becomes stronger. In 2H phases, the dominant peaks of sulfur K edge spectra originate from unoccupied d bands. Further, the broad peaks at higher energy ranges are due to the transitions to sulfur p hybridized with M-s and p states. For energies below 7eV, M-d state is the target state of most of the transitions in both 1T and 2H phases. For above 10eV energies, however, sulfur-d is the target state. Moreover, density of states of sulfur-p (d) is very similar in shape to that of sulfur K (L2,3 ) edges spectra. For the sulfur L2,3 edges, from 2H-TaS2 to 2H-VS2 and also from bulk to monolayer, the number of transitions to M-d state increases.